Extending prior work on environmental influences in financial decision-making, this study hypothesizes an adverse association between air pollution and individual investors’ trading behavior. Leveraging a proprietary dataset of granular transaction records, we demonstrate that elevated pollution levels significantly reduce individuals’ propensity to buy stocks while increasing their disposition to sell. These effects exhibit pronounced heterogeneity across investor sophistication, security characteristics, and regional pollution exposure—with particularly strong impacts among novice investors and residents of high-pollution urban centers. Our findings provide the first micro-level evidence linking air quality to retail trading strategies, thereby advancing the literature on environmental finance and behavioral biases.